In a vehicle known from prior art for heating the input air for the passenger compartment, waste heat from the engine is used. By means of the coolant converted in the engine cooling circuit, the waste heat is brought to the cooler of the air conditioner, and there transferred via the heating warmth exchanger to the air flowing into the passenger compartment.
Known facilities with coolant-air heat exchangers, which relate to the heating performance from the cooling circuit of an efficient internal combustion engine of the vehicle prime mover, no longer attain the temperature level required for comfortable heating of the passenger compartment when the ambient temperature is low, to cover the overall heating requirement of the passenger compartment. The same holds true for facilities in vehicles with hybrid propulsion.
When the overall heating requirement of the passenger compartment cannot be covered by the heat from the engine cooling circuit, heating measures such as electrical resistance heating (ERH) or fuel heaters are required. A more efficient option for heating of air for the passenger compartment is a heat pump with air as the heat source, in which the refrigerant circuit serves both as the sole heating means and also as a heating measure.
Prior-art air-air heat pumps, which are configured for the combined cooling-unit and heat-pump mode, and consequently also for the heating mode, admit the heat from ambient air.
Heat pump systems in which the output is transferred between the refrigerant and air often cannot simultaneously heat and dehumidify the air brought into the vehicle. The result of this is that the air conditioner of a vehicle cannot be operated with recirculated air at low ambient air temperatures. With recirculated-air operation, the air recirculates out of the passenger compartment. Due to the lack of a dehumidifying function, the remaining air humidity as well as the water emitted by the occupants in the form of vapor would lead to a misting up of the windows.
In traditional air conditioners, when the ambient temperature is above 20° C. and after thermal comfort has been reached, the air fed into the passenger compartment is cooled by about 3° C. to 10° C. and dehumidified in the process, and then heated up with a slight heating to the desired temperature of additional air. A target temperature for the passenger compartment of about 20° C. to 25° C. is, for example, intrinsic to thermal comfort.
Glycol-air heat pumps use the coolant of the internal combustion engine, which mostly corresponds to a water-glycol mixture, as the heat source. With this, heat is withdrawn from the coolant. As a consequence of this, the internal combustion engine is run for a longer time at low temperature, which has a negative effect on exhaust emissions and fuel consumption. Due to the internal combustion engine operating intermittently in hybrid vehicles, during longer trips the coolant temperature does not become sufficiently high. As a consequence, the internal combustion engine is subjected to a start-stop operation at low ambient temperature. The internal combustion engine is not shut off.
In DE 10 2010 024 775 A1, a device is described for air conditioning of vehicles, which is operable both in the heating and in the cooling mode. The device exhibits a refrigerant circuit, which comprises a thermal environment module with a condenser for heat exchange with the ambient air, a thermal passenger-compartment module with a vaporizer and a heat register for treatment of feed air for the passenger compartment, an expansion module with an expansion valve, and a compressor for compressing the refrigerant. In addition, the device is configured with a fluid heat exchanger which is linked with a connectable fluid circuit independent of the refrigerant circuit. The components can be switched with aid of valves so that the refrigerant can admit heat in the heating mode via the connectable fluid heat exchanger or the condenser of the ambient module, or via both, which in turn can be exchanged with the inserted condensation energy via the passenger compartment module to the passenger-compartment feed air.
EP 0 913 282 B1 discloses an air conditioner for a motor vehicle with a refrigerant circuit comprising a compressor and a first cooler, a first condenser, which is placed with a heating core of an engine cooling circuit in an air flow channel, a second condenser, and a second cooler, which are jointly arrayed in a second air flow channel. The second cooler and the second condenser are configured in fluid-connected fashion as well as switched parallel to the first condenser. The refrigerant circuit is configured for a combined cooling and heating operation. A third condenser is fluid-connected with the second condenser and has the coolant of an engine cooling circuit flowing through it. Additionally the air conditioner exhibits a control device which is configured for controlling the flow of the engine cooling medium and/or of the refrigerant, depending on the thermal loading state of the vehicle in correspondence with the discharge pressure of the compressor. When it goes below the limit value for the compressor discharge pressure, the compressor stops operating.
In DE 10 2010 024 853 A1, an air conditioner is disclosed with a refrigerant circuit, which comprises a condenser for taking a refrigerant in by suction, compressing it and ejecting it, an external heat exchanger for transferring heat between the refrigerant and the outside air, as well as two inner heat exchangers for transferring heat between the refrigerant and the air to be fed into the passenger compartment. In addition, the air conditioner exhibits refrigerant circuit switchover devices which are suited to switch the refrigerant circuit between the cooling mode and a heating mode. The refrigerant circuit switchover device is configured with several electromagnetic valves, which can be switched into a preset opened or closed state. Exterior air serves as the sole heat source.
The task of the present invention is to further develop the method for operating an air conditioner with a refrigerant circuit for the combined cooling-device and heat pump mode as well as a post-heating mode for heating, cooling and dehumidifying the air to be treated for the passenger compartment, especially of motor vehicles with an insufficient heat source from the prime mover. High-level operating safety is thereby ensured with minimum expense. The air conditioner should be able to be operated with high efficiency in the various operational modes.